A hybrid bicycle is a bike for general purposes. It can be used on a wide variety of surfaces such as paved and unpaved roads and on trails. It has features from the road bike and the mountain bike and gives you a more upright posture while riding.
The Commuter Bike
This hybrid can be used for commuting. Normally it has derailleur gearing and fairly light 28 mm tires. They have front and rear lights so you can use it early in the morning or in the evening hours when it is getting dark.
The City Bike
It is designed for urban commuting and you have an upright position. It has a strong but lightweight frame and wide heavy belted tires. They usually have front and rear lighting systems so you can use them at night. Sometimes it has a system used to suspend the rider in order to protect him from the roughness of the road.